This invention relates to a method and apparatus of reducing the trolling speed of boats having inboard engines The invention has particular application to fishing boats which often are used to troll for fish using live bait. Inboard engines have a minimum idle r.p.m. below which the engine will either stall or overheat. This idle r.p.m. generally ranges between 600 and 800 r.p.m., and translates to an idle speed of approximately 3-4 knots. This speed is substantially too fast for effective fishing according to the trolling method, because the boat is moving so fast that the live bait drowns.
There are two known prior art methods of reducing the trolling speed of boats with inboard engines. One method involves the installation of a trolling valve on the gear redirects hydraulic fluid allowing the clutch of the gear to slip, thereby reducing the output r.p.m. of the shaft. As noted above, this can cause mechanical problems with the gear. In addition, trolling valves reduce the trolling speed of the boat only about 30%.
The other method involves repeatedly putting the transmission into and out of gear. This creates substantial additional wear on the transmission.
There is a method of reducing the speed of outboard engines on much smaller boats which involves hanging a baffle plate in the propeller wash of the outboard engine. The baffle plate is mounted on the drive housing above the propeller and is vertically moveable between a raised position in the water but out of the propeller wash, and a lowered position in the water in the propeller wash. The baffle plate is raised and lowered by a cable which connects to the baffle plate and extends into the boat. This device is shown in U.S. Pat. No. 3965838. This type of device is not practical for large boats of the type which have inboard engines.
The present invention provides an effective means of safely reducing the trolling speed of boats having inboard engines without modifications to the gear or to the engine operation.